Methods and devices utilized for determining concentrations of electroactive species in solutions using electrochemical or electrolytic methods are well known. These instruments typically include a pair of electrochemical half cells, one of which is used as the sensor or sample half cell and the other as a reference electrode or a reference half cell. As is the case with any concentration determination of dissolved gaseous species in a liquid, the temperature at which the electrochemical determination is made needs to be known. Traditionally, blood gas determinations, for example, have been made utilizing permanently installed laboratory instrumentation to which samples are brought for analysis. Of course, in such instruments the temperature at which the sample is analyzed can be readily controlled, for example, by a constant temperature oven. These types of methods have disadvantages for portable devices. One such disadvantage is that portable devices cannot contain constant temperature ovens. Known temperature control systems for portable devices also have disadvantages. One such disadvantage is that they typically have limited operating temperature ranges. Another disadvantage is that such systems are susceptible to outside interferences. Therefore, improvements are desirable.